"The rich are different from you and me," declared F. Scott Fitzgerald. "They behave like Katharine Hepburn."

All right, the second half of that quote is my invention, but Fitzgerald could have said it, and it would have been true. Everything about Hepburn bespoke familiarity with ease and comfort from the cradle on: the vaulted cheeks, the Seven Sisters accent, the money-in-her- voice self-confidence, the inextinguishable joie de vivre, the indifference to convention - all of which are on display in her classic heiress performances, as Susan Vance in Bringing Up Baby and Tracy Lord in The Philadelphia Story.

A. Scott Berg had long wanted to meet Hepburn. After a couple of near-misses, he scored in 1983, when she agreed to be interviewed by him for a magazine article. Although she was more than 40 years his senior, they hit it off so well that soon she was telling him, "You are me."

The intensity of their rapport comes as a bit of a surprise. Hepburn was famous for her whirlwind, carpe diem approach to life, while Berg is known as a craftsman of the planned, stately career. Here is a man who mapped out his life's work as an undergraduate - writing definitive biographies of 20th-century American VIPs - and has been following through ever since. (So far he has polished off Maxwell Perkins, Samuel Goldwyn and Charles Lindbergh, with Woodrow Wilson in progress.)

Initially at least, the friendship seems to have been a case of attracted opposites: Old hell-raiser meets young fogey.

But Berg had brought more than just a solid reputation to his first encounter with Hepburn. Instinctively, he knew how to charm her. When she subjected him to a volley of commands and questions, he returned her fire.

Asked if he smoked, he replied, "No, Lady Bracknell, I don't." She laughed. A few get-togethers later, she said, "Look, I think you should call me Kate." "OK, Kate," he told her. "And I think you should call me ... Mr. Berg." His inspired sassiness seems to have delighted her.

As has been widely reported, the star and the scribe agreed that their periodic chats in her New York town house and at the family cottage in Connecticut should be the basis for a book, to appear only after Hepburn's death, lest she feel inhibited by prospects of hurt feelings or embarrassment.

But not too long afterward - she wanted their version of her life to set the right posthumous tone, scooping other interpreters and biographers. Berg's timing was impeccable. Four years ago, when Hepburn's decline became so pronounced that it was clear he had learned everything she could tell him, he began writing. He finished the manuscript and put it aside. Three weeks ago, at age 96, its subject in effect gave her imprimatur. Berg added some final thoughts, and Kate Remembered went forth.

It resembles another book about a venerable Hollywood figure, Cameron Crowe's Conversations with Wilder. Both are biographies without tears - abbreviated, informal, fast-moving. Given the daunting length of so many biographies nowadays, this is not a bad way to go.

The central virtue of Kate Remembered is the author's generosity with his insider's privileges. Care to know what Hepburn typically served for snacks at cocktail time? The answer is here: "small shrimp with a Louis sauce . . . and small hot dogs with honey mustard."

Ever wondered what Kate thought of the other stellar Hepburn? Berg doesn't leave you guessing. When Kate received a letter informing her she had won a fashion award, he asked, "Are you sure they didn't mean Audrey?" Kate's response was to shove an ice-cream cone in his face.

The reader takes vicarious pleasure not only in Berg's closeness to Hepburn but in her connections to practically everybody.

In one lovely interlude from the late 1980s, the annuated Hepburn agrees to be an emissary to the superannuated Irving Berlin, whom Berg wants to interview for his Goldwyn biography but who has repeatedly nixed direct appeals. Though she hasn't seen Berlin since the '30s, when they worked together at RKO, Hepburn simply marches over to his house one day and rings the doorbell.

She assures the maid that she only wants to know how Mr. Berlin is doing, but Berlin - his hearing evidently still sharp - recognizes her voice. "Kate is that you?" he yells from several floors up. He insists that she stay for tea, and the two former colleagues spend three hours regaling each other with memories of old times.

In the end, however, she fails in her mission. Berlin explains that the very thought of Goldwyn gets his stomach "churned up," and he is unwilling to dredge up that portion of the past. Then he goes on to do just that, with her. His Goldwyn stories "were very funny, just killingly funny," she later confesses to Berg, "and I was having such a good time I don't remember a goddamned one of them."

Years later, the roles are reversed, with Berg serving as go-between for Hepburn and Warren Beatty, who wants her to play a small part in his 1994 remake of Love Affair. In the end, she agrees, but not without taking the measure of Beatty's alleged charm.

To Berg's observation that Beatty and his wife, Annette Bening, seem very much in love, Hepburn replies, "With the same man." And after Beatty exclaims to Hepburn, "If I had only met you thirty years ago," Hepburn privately asks Berg, "Was that supposed to be a compliment?"

Berg's writing ranges from poetic to careless (dangling participles, use of "like" when "as with" or "as in" is required). Contrary to Berg's assertion, the director John Ford was born John Martin Feeney, not Sean Aloysius O'Fearna (the authority is Ford's most recent biographer, Joseph McBride). And at times the book threatens to morph into a dual biography - of Hepburn and her friend Irene Mayer Selznick, the daughter and wife of Hollywood moguls.

But Berg's keen powers of observation and shrewd readings of his "characters" are evident on every page. The only sizable disappointment is the blank space at the end of Hepburn's long intimacy with her great love Spencer Tracy. Hepburn wouldn't talk about the last five years of their life together, leading up to Tracy's death in 1967 - and that, as she might have remarked, is that.

Hepburn may or may not have been the greatest actor of Hollywood's golden age, but Berg's claim that she carved out "the greatest acting career of the twentieth century" seems incontestable. In writing this book, he has given that career a last jolt.

It's no soft-soap job. Hepburn had her faults - notably the selfishness that she acknowledged in retrospect - and Berg reports even the time he caught her rifling through his overnight bag. But Kate Remembered is her last performance, and one of her most touching. That it comes to us from beyond the grave, and immediately, should not be a shock.

That's the sort of thing a goddess does.

Dennis Drabelle is a contributing editor for The Washington Post Book World.